Collect total number of CPU cores and available RAM for each build.

Collect the total number of CPU cores and available RAM for each build
as part of the system resource info. This is to know what kind of
build machines that the developers are using.

Bug: b/169453825
Test: m nothing and ran printproto on soong_metrics to validate the
      data.
Change-Id: I8617bdb9490b37d7689abd27d349af1a651533db